Classifying Bacteria Flashcards
(30 cards)
What is microbiology and what is a microbe?
Microbiology → the study of microorganisms
Microbe → any organism that is too small to be seen clearly by the unaided eye, ie. less than around 0.1mm. They are usually single cells or small clusters of cells.
This includes prokaryotes (bacteria and archaea), eukaryotes (algae, fungi and protozoa) and viruses.
What are the main features of a prokaryote?
Small, a few μm in length
No organelles but can sometimes have internal membrane systems with specialised functions eg. no mitochondria but aerobic prokaryotes carry out respiration in the plasma membrane, thylakoids can carry out respiration and photosynthesis.
70S ribosomes
Flagella is a single filament made up of flagellin, which is attached to a free spinning rotary motor.
Bacteria have a peptidoglycan cell wall, while archaea can have various types.
What are the main features of a eukaryote?
Large, tens of μms
Have mitochondria, nucleus, ER, Golgi body, centrioles etc
Plants, algae and some protists have plastids
Chloroplasts have a double membrane and are the site of photosynthesis. They are present in photosynthetic eukaryotes but absent in prokaryotes.
80S ribosomes in the cytoplasm
70S ribosomes in organelles (eg, mitochondria, chloroplast)
Flagella are a bundle of microtubules in a 9+2 formation, surrounded by a membrane sheath. The microtubules move relative to each other to provide movement.
Plants and most algae and a cellulose cell wall, while fungi have a chitin cell wall.
How is DNA packaged in prokaryotes?
No nuclear membrane
No chromosomes
No mitosis or meiosis (divide by binary fission)
No microtubules
DNA is typically circular and exists as one or more copies (of the same genetic code) per cell. This is the nucleoid and has 2 - 10 Mbp, including for 1000 - 5000 proteins coding genes
Plasmids (small circular DNAs that carry non-essential genes that may advantageous) are often present
How is DNA packaged in eukaryotes?
DNA (excluding organellar DNA) is contained within a double-membraned structure called the nucleus
DNA is 10 - 10,000 Mbp long and there are 6000 - 40,000 protein coding genes
Nuclear DNA is divided into a number of linear molecules
DNA is then packaged into elaborate protein-DNA (through binding to histones then compacting) structures called chromosomes
Chromosomes are attached to microtubules on the spindle during cell division
What is endosymbiotic theory?
The theory that eukaryotes are made up of 3 bacterial cells:
archaeon + alpha-proteobacterium (forms mitochondrion) + cyanobacterium (forms chloroplast)
These cells formed a symbiotic relationship millions of years ago and are now one cell.
Evidence for this is that both mitochondria and chloroplast contain their own DNA with a transcription/translation system like that of prokaryotes
What are the two different types of medium that bacteria can be grown on, and what are their advantages and disadvantages?
Defined medium → assembled from a specific list of chemicals
Cannot use when specific growth factors are unknown, but provides all the nutrition the colony needs
Undefined medium → includes undefined things, eg. meat broth, yeast extract, blood products etc.
Easier to grow colonies on, but other unwanted colonies may also grow because the medium is not sterile.
How can colonies be characterised by morphology?
Colonial morphology → characterised by the appearance of the colony on a specific medium under specific conditions
shape, colour, texture, size smell, form, elevation etc
Cell morphology → appearance of cells under a microscope
spherical (cocci), rods, comma-shaped (vibrio), spiral (spirillum), budding, appendaged, filamentous
Cell arrangement → depends on pattern of cell division
can be 1D (straight line), 2D (divide in 2 directions) or 3D (form a 3D bundle of cells)
How can cells be fixed to a slide in order to be observed under a microscope?
Heat fixation → gentle flame heating
This preserves the overall morphology but destroys the structures within the cell
Chemical fixation → chemicals that penetrate cells and react with cellular components eg. ethanol, formaldehyde (methanal)
This preserves fine cell structure
What is differential staining?
The separation of bacteria into different groups based on their staining properties.
This is particularly helpful when different colonies are the same shape, and so would not be able to be identified through normal staining.
What is acid-fast staining?
1 → Smear bacteria on a Petri dish and stain with hot carbol fuchsin.
2 → Wash with water
3 → Soak in 20% H2SO4 for 10 minutes
4 → Wash again with water
5 → Counterstain with methylene blue.
The bacteria with high lipid content in their cell walls will take up the first stain, and the ones that don’t will take up the blue stain.
What is gram staining?
Gram staining distinguished bacteria based on their cell wall structure, ie. whether they are gram + or gram -
1 → Bacteria is smeared onto a Petri dish, heat-fixed and then stained with crystal violet.
2 → Add Iodine or KI which forms a crystal violet / iodine complex, preventing the stain from leaking
3 → Wash with solvent, usually 95% ethanol
4 → Stop with water
5 → Counterstain with a different colour
Crystal violet stains gram + bacteria because the alcohol dehydrates the cell wall and traps the strain
The other dye stains gram - because the alcohol dissolves the outer membrane, allowing the dye to leak and the other stain to stay
What are the 8 ways bacteria can be classed using physiology?
Nutritional requirements
Light
Temperature
Salinity
pH range
Oxygen
Pressure
Toleration of chemical inhibitors
What is the difference between a diazotroph and an auxotroph?
Diazotroph → nitrogen-fixing bacteria
Auxotroph → A microbe that requires additional growth factors, such as vitamins and amino acids
What is the difference between an obligate microbe and a facultative microbe?
Obligate → microbe needs that factor to live
Facultative → microbe is able to use alternative growth mechanisms if that factor is in low supply
What is the difference between a psychrophile, a mesophile and a thermophile?
Psychrophile → microbe grows at low temperatures eg. bacteria in polar regions, deep in the sea
Mesophile → microbe grows at average temperatures eg. bacteria in the gut
Thermophile → microbe grows at high temperatures eg. in hot springs, volcanic regions
What is the difference between a halophile, an acidophile and an alkaliphile?
Halophile → microbe that can live in a very salty environment
Acidophile → microbe that can live in a very acidic environment eg. in the human stomach
Alkaliphile → microbe that can live in a very alkaline environment eg. in soda lakes
What are the different types of aerobes and anaerobes?
Obligate aerobe → needs oxygen to survive
Obligate anaerobe → cannot survive with oxygen present
Facultative aerobe → can survive without oxygen but use it when available
Aerotolerant anaerobe → can survive with oxygen present but don’t need or use it
Microaerophile → damaged by normal oxygen levels so can only survive at low oxygen levels
What is a barophile?
A microbe that grows best at high pressures.
An extreme barophile is a microbe that cannot survive at atmospheric pressure.
Most barophiles are psychrophiles as well.
How can bacteria be classified based on their toleration of chemical inhibitors?
Respiratory inhibitors → eg. gram + bacteria are resistant to NaN3, while gram - bacteria are sensitive to it.
Chaotrophic agents (substances that cause proteins to denature) → eg. Phenol usually breaks up the cell by denaturing the plasma membrane, enabling the DNA to be extracted. Pseudomonas, however, are resistant to phenol because they use it as a source of C.
Antibiotics → eg. Mycoplasma lack a cell wall and so they are resistant to penicillin.
What is the minimum inhibitory concentration (MIC)?
The point at which bacteria will start growing for that antibiotic.
How can a colony be tested for the products of sugar fermentation?
1 → Inoculate the colony in a liquid medium with sugar, a pH indicator and a Durham tube.
2 → Incubate the colony for 24 hours.
3 → If organic acids are produced, the pH indicator will turn red. If gases are produced, they will collect in the Durham tube.
How can a colony be tested for fermentation or oxidation?
1 → Inoculate the colony in soft agar along with glucose and pH indicator. The soft agar produces an oxygen gradient down the test tube.
2 → Incubate for 24 hours
3 → If the colony respires oxidatively, only the top of the agar near the surface will have turned red because they can only survive in conditions with high oxygen levels.
4 → If the colony respires using fermentation, all of the agar will have turned red.
What is the catalase test?
It tests for whether the isolate produces catalase or not.
Hydrogen peroxide is added to the cells; if bubbles are produced then the colony is catalase positive (eg. Staphylococci), but if bubbles are not produced then the colony is catalase negative (eg. Streptococci)
